Gas insulated flexible high voltage cable

ABSTRACT

A gas insulated flexible high voltage cable in which an annular conductor is positioned within an annular conductive enclosure. Spacer means position and maintain the conductor within the annular conductive enclosure. The spacer means comprises a plurality of gas permeable support layers of porous material, spaced one from another, and a plurality of perforated conductive layers alternately positioned between each pair of support layers. The spacer means is saturated by a volume of compressed insulating gas, such as sulfur hexafluoride.

United States Patent [1 1 McConnell GAS INSULATED FLEXIBLE HIGH VOLTAGE CABLE [75] Inventor: Lorne D. McConnell, Radnor, Pa.

[73] Assignee: I-T-E Imperial Corporation,

Philadelphia, Pa.

[22] Filed: Jan. 17, 1972 [21] Appl. No.: 218,277

174/25 G, 26 G, 16 B, 99 B, 15 C, 110 F, 122 R, 120 R, 120 SR, 1201 C, 120 PP, 130

[56] References Cited UNITED STATES PATENTS 2,799,720 7/1957 Emanueli 174/25 G 2,147,402 2/1939 Faucett 174/25 G 2,286,052 6/1942 Beaver et al 174/25 G 3,160,703 12/1964 Muller 174/120 R 2,531,156 11/1950 Piercy et a1.... 174/25 G X 2,782,248 2/1957 Clark 174/25 R 3,459,871 8/1969 Eager, Jr. at al 174/25 R Oct. 23, 1973 Primary Examiner-Bernard A. Gilheany Assistant ExaminerA. T. Grimley AttarneySidney G. Faber et a1.

[57] ABSTRACT A gas insulated flexible high voltage cable in which an annular conductor is positioned within an annular conductive enclosure. Spacer means position and maintain the conductor within the annular conductive enclosure.

The spacer means comprises a plurality of gas permeable support layers of porous material, spaced one from another, and a plurality of perforated conductive layers alternately positioned between each pair of support layers. The spacer means is saturated by a volume of compressed insulating gas, such as sulfur hexafluoride.

8 Claims, 4 Drawing Figures '1 GAS INSULATED FLEXIBLE HIGH VOLTAGE CABLE BACKGROUND OF THE INVENTION This invention relates to power cables, and is particularly directed to gas insulated high voltage power cables of simple construction, capable of conducting heavy currents at high voltages.

In current gas insulated transmission systems, a coaxial conductor is carried in a metal housing and held in position with respect thereto by solid insulating discs of the type disclosed in U.S. Pat. No. 3,573,341 to Graybill et al., and assigned to I-T-E Imperial Corporation. Such discs position, maintain and support the coaxial conductor within the housing.

Such prior art systems can, however, only be manufactured and shipped in relatively short lengths of about 40 feet, and must thereafter be field assembled, field cleaned and field tested. These arrangements, moreover, include a large gas-filled volume in which loose conductive dust particles may become charged and thereafter oscillate through the system to establish points of high dielectric stress which may cause local electrical breakdowns within the system.

According to this invention, these disadvantages may be overcome by replacing the spacer discs with a composite spacer means which substantially fills the volume between the annular conductor and conductive housingQOther advantages of this invention will become apparent from the more detailed description that follows.

SUMMARY OF THE INVENTION Briefly, the gas insulated, flexible, high voltage cable comprises an annular conductive enclosure, gas impervious throughout its length. An annular conductor is positioned within the annular conductive enclosure. Spacer means position and maintain the conductor within the annular conductive enclosure.

The spacer means, itself, comprises a plurality of gas permeable support layers of porous material, spaced one from another. Each gas permeable support layer surrounds the annular conductor and each preceding support layer. A first gas permeable support layer not only surrounds the annular conductor, but it also engages the annular conductor.

A plurality of perforated conductive layers are alternately spaced between the gas permeable support layers. The succession of alternating support layers and perforated conductive layers form a composite structure.

A gas, for instance, sulfur hexafluoride, trichlorofluoromethane, dichlorodifluoromethane, dichlorofluoromethane, chlorodifluoromethane and the like, is dispersed under a controlled positive pressure throughout the spacer means and is adsorbed in the gas permeable support layers. Gas pressure within the spacer means may vary from I to 6 atmospheres and preferably vary from 2 to 4 atmospheres. The gas permeable support layers within the spacer means are in gastransfer communication with each other. These support layers are themselves gas permeable and porous and gas may communicate between support layers through the perforations provided in the conductive layers alternately spaced between the support layers.

The gas permeable support layers are preferably formed of an open cell, flexible foam resin material, for instance urethane (castor oil, polyester and polyether singly or in combination) polyethylene, styrene or silicone, but these support layers may be formed, as well, from materials such as cloth, paper, felt or like materials that have an open structure. The fibers in these other suitable materials may be either natural or synthetic provided they impart, to the spacer means, acceptably large surface area and volume resistivity, and an acceptably low dielectric constant and a creep-age path substantially greater than the direct radial distance from conductor to ground.

The materials used to form different support layers within the spacer means may be varied to preferably provide a dielectric constant in the spacer means of about 1.05 to 2.0. In a more preferred spacer means embodiment, the composition of support layers may be varied to provide a dielectric value approaching 1.05 at the outer layer of the spacer means and a maximum dielectric value approaching 2.0 at the inner layer of the spacer means proximate to the annular conductor.

The compressed gas saturated spacer arrangement substantially inhibits the oscillation of metallic dust particles between the annular conductor and annular conductive enclosure. The tendency for an electrical breakdown to occur is therefore reduced. The spacer arrangement acts like a microporous filter to trap particles enclosed within the volume defined between the annular conductive enclosure and annular conductor. The filter-like effect of the spacer means prevents any significant accumulation of migrating particles, even over long cable sections. By virtue of this cable construction, trapped particles are no longer free to oscillate between the two concentric conductors to reduce the dielectric breakdown level of the cable section.

BRIEF DESCRIPTION OF THE DRAWINGS This invention may be more fully understood in conjunction with the following drawings in which:

FIG. 1 is a vertical cross-section illustrative of the prior art in which a solid insulating disc supports and maintains a coaxial conductor in position in a metal housing;

FIG. 2 is a detail view of the disc shown in FIG. 1;

FIG. 3 is a detail cut away view in section of one embodiment of this invention; and

FIG. 4 is an elevated end view of the embodiment shown in FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION FIGS 1 and 2 illustrate prior art cable constructions and the spacer means used to support the annular conductor within the annular conductive enclosure. The compressed gas insulated conductor 10 is normally comprised of a metal enclosed high voltage electrical conductor in which a hollow metallic conductor 12 is centrally supported with a surrounding grounded metal enclosure 14 by means of a disc-shaped insulator 16. The interior hollow space between the hollow metallic conductor and grounded metal enclosure is usually filled with a high dielectric compressed gas, such as sulfur hexafluoride. Prior art constructions of this type provide a large volume through which metallic dust particles can oscillate to establish a point or points of high dielectric stress. These metallic dust particle accumulations probably reduce the dielectric breakdown voltage and cause local breakdowns to occur on succeeding over voltage surges on the system.

Referring now to FIGS 3 and 4 which illustrate an embodiment of the present invention, annular conductor 20 is formed of large diameter stranded aluminum hollow cable 22 which-is flexible and lightweight. The aluminum stranding may be wrapped over a lightweight hollow core 24 for additional support, if necessary. Aluminum stranding 22 is housed in conductor jacket 26. Conductor jacket 26 is a high dielectric constant and low resistivity material. It is desirable that the conductor jacket be formed of a material with such properties to obtain a minimum voltage gradient across its thickness. The character of the material from which the conductor jacket is forrned is such that the material is compatible with refrigerant gases and sulfur hexafluoride.

Insulation support layers 28 which surround conductor 20 are formed of an open cell flexible foam resin material. Suitable resin materials from which the insulation support layers may be formed typically include urethane, silicone, polyethylene, styrene and their derivatives and copolymers.

Numeral 30 designates the perforated conductive layers alternately positioned between the insulation support layers 28. The conductive layers 30 may be a metallic or conductive tape lap-wound between the support layers at controlled diameters with respect to annular conductor 20. Alternatively, the conductive layers may be formed by applying a conductive coating to a thin insulating film. The helical windings are perforated to provide for the communication of insulating gas between different layers in the composite spacer means. The number and position of conductive foils in the composite spacer means may be varied along with ers 28 are illustrated as helically wound strips; however, the structure of the support layer may vary.

Annular conductive enclosure 32 houses annular conductor 20 and composite spacer means 34. Annular conductive enclosure 32 comprises conductive inner jacket 36 which may be lap wound around the spacer means or may be an integral extruded layer. Inner jacket 36 may be formed of any conventional conductive materials which are impervious to the insulating gas confined within the spacer means characterized by a low resistance to provide an effective ground layer for the insulating system. Banding 38 is a non-magnetic stainless steel wire which adds structural strength to inner jacket 36. Other equivalent materials may be used to band inner jacket 36. Outer jacket 40 houses the entire cable assembly. It is a wrapped or extruded covering whichsecures banding38 to inner jacket 36 and protects the entire cable assembly from weather conditions and external abrasion.

The spacer means 34 is gas filled, preferably with sulfur hexafluoride gas. However, other insulating gases with high dielectric strengths may be used in place of sulfur hexafluoride. The gas is maintained within the spacer means 34 under controlled pressure of about 2 to 4 atmospheres. The insulating gas, may diffuse throughout the total volume of spacer means 34 through porous insulation support layers 28 and perforated cond enser layers 30.

Spacer means 34 is sufficiently porous to permit a substantially uninhibited movement of compressed gas from bus section to bus section in the cable arrangement, but the spacer means is not porous enough to permit unrestricted passage of the metallic dust particles which may be present in the conductor, or which may be generated by the interaction of voltage polarity which is on a conductor.

While the present invention has been described with reference to specific embodiments, these embodiments are provided for illustrative purposes only, and are not to be construed as limiting the invention, which is defined by the appended claims.

What is claimed is:

1. A gas insulated flexible high voltage cable comprising:

an annular conductive enclosure, gas-impervious throughout its length,

an annular conductor positioned within said enclosure; and spacer means positioning and maintaining said conductor within said enclosure;

said spacer means having a dielectric constant of about 1.05 to 2.0 and consisting essentially of a plurality of gas permeable support layers of porous material, spaced one from another, surrounding said conductor and providing support therefor, 21 first gas permeable support layer engaging said conductor; and a plurality of perforated conductive layers alternately spaced between said gas permeable support layers.

2. The gas insulated flexible high voltage cable of claim 1 including a gas under controlled positive pressure dispersed throughout said spacer means and adsorbed in said gas permeable support layers, said gas permeable support layers being in gas-transfer communication, one with another.

3. The gas insulated flexible high voltage cable of claim 2 wherein said gas is sulfur hexafluoride.

4. The gas insulated flexible high voltage cable of claim 1 wherein said porous material from which said gas permeable support layers are formed is selected from the group consisting of open cell flexible foam resins, cloth, paper and felt.

5. The gas insulated flexible high voltage cable of claim 1 wherein said annular conductor comprises an annular conductive housing; and v a plurality of stranded conductors confined within said housing.

6. The gas insulated flexible high voltage cable of claim 1 wherein said annular conductive enclosure comprises a conductive inner jacket impervious to said gas;

an outer jacket surrounding said conductive inner jacket; and

conductive, non-magnetic banding between said conductive inner jacket and said outer jacket.

7. The gas insulated flexible high voltage cable of claim 1 wherein said porous material from which said gas permeable support layers are formed is an open cell flexible urethane foam.

8. The gas insulated flexible high voltage cable of claim 1 wherein the dielectric constant of the individual layers of said spacer means is varied such that it approaches 1.05 at the outermost layer thereof and approaches 2.0 at the innermost layer thereof proximate to said annular conductor. 

2. The gas insulated flexible high voltage cable of claim 1 including a gas under controlled positive pressure dispersed throughout said spacer means and adsorbed in said gas permeable support layers, said gas permeable support layers being in gas-transfer communication, one with another.
 3. The gas insulated flexible high voltage cable of claim 2 wherein said gas is sulfur hexafluoride.
 4. The gas insulated flexible high voltage cable of claim 1 wherein said porous material from which said gas permeable support layers are formed is selected from the group consisting of open cell flexible foam resins, cloth, paper and felt.
 5. The gas insulated flexible high voltage cable of claim 1 wherein said annular conductor comprises an annular conductive housing; and a plurality of stranded conductors confined within said housing.
 6. The gas insulated flexible high voltage cable of claim 1 wherein said annular conductive enclosure comprises a conductive inner jacket impervious to said gas; an outer jacket surrounding said conductive inner jacket; and conductive, non-magnetic banding between said conductive inner jacket and said outer jacket.
 7. The gas insulated flexible high voltage cable of claim 1 wherein said porous material from which said gas permeable support layers are formed is an open cell flexible urethane foam.
 8. The gas insulated flexible high voltage cable of claim 1 wherein the dielectric constant of the individual layers of said spacer means is varied such that it approaches 1.05 at the outermost layer thereof and approaches 2.0 at the innermost layer thereof proximate to said annular conductor. 